I use a magnifier app and an iPhone 5. Although I just got an iPhone 8 so maybe they will get a little better. Maybe that will help my pics, which are OK at best. I do know that the advice here has made them 100% better than when I started.
Yes, the OP link. The first post asked if a used Sony HX350 would be a good camera for the purpose. Since this and a thousand other models have never been touched by me, I can not answer but the camera has few things that makes me want to spend $200. I find it odd that the used price range of the Canon model T3i mentioned is huge on eBay. Buyers of used cameras always need to beware. I am not going in the business of trying to shoot with every camera out there so I can not help equipment buyers except those interested in what I use (Canon DSLR's).
I use a 12 yo Nikkon 8700 which cost me around $900 at the time, should be less than $100 to find one now. I wouldn't mind upgrading but it works for the moment. Probably one of my favorite photos
My first digital camera was a Nikon Coolpix 990. I used it to take the photos for Victor Failmezger's book and thought the photos were decent then. Mine still works. Used ones are cheap. The 8700 was a newer model I never had. If you can live with the photo below, it might be a good cheap choice.
Plastic stands like that are good for imaging coins. Inexpensive and get the right angle in the light, or at least with my small setup.
While it is not anything approaching as sharp as my camera images and would not make large prints, I was surprised at my first try using my cell phone. This was shot laying the phone on top of the inverted plastic flower pot I use for shading the background of camera photos and using the Galaxy S8 magnifier tool. I don't see myself playing with this more but I can see how it might serve someone determined to avoid using a camera. Of course you still need to shot both sides and combine them into one file.
It is surprisingly easy to combine smartphone images using apps. On iPhone there is an app (maybe on Samsung/Android not sure though) called Pic Stitch. When you open it up, select the template below the first one (has two vertical rectangles). Select aspect on the bottom bar, select the third option (2x1). Then select your images by hitting the plus sign in the middle of the squares. To combine black images without a white barrier you have to purchase the layers extension (if thats what it's called) for 99 cents. Totally worth it imo.
I use a high definition setup, and it can slow you down. If you're looking for shots that will get your point across for this list, then use an iPhone and learn how to control the lighting. Lighting matters more than loading up with high grade gear. Using a phone is a lot faster than really critical work will be, so you can contribute decent pics to more of the threads in a timely way. Just be aware that for really critical work that needs to be enlarged to show the details you want, the phone images will "fuzz out" a lot sooner than a pic from a hi-def system.
For under 50 USD the Canon S2 IS powershot maybe the better budget macro camera.The S2 apparently focuses down to 0.0 mm in super macro mode with an object 22 x 16 mm in size filling the frame.. Maybe a good option to learn the basics and upgrade with your needs. Its not a huge investment even with tri-pod and lighting kit. Not sure any other camera can offer one to one ratio macro images at that price.